The present invention is concerned with a buried butted contact. More particularly, the present invention is concerned with providing an ohmic contact through shallow trench isolation of an n-type diffusion to ground or a type diffusion to Vdd. The buried contact of the present invention is vertically displaced from the top surface of the substrate and permits the contact to be formed in reduced area. The buried contact of the present invention does not extend to any significant extent under the active surface diffusion. According to the present invention, a buried diffusion is contacted below the surface of the substrate to surface diffusion of an opposite polarity type by a metallic-type interconnection line. The metallic-type interconnection line can be a metal, a metal alloy, and/or an intermetallic silicide. The present invention is also concerned with a method for fabricating the buried butted contact.
Butted contacts have been used for contacting n-type diffusion to ground or a p-type diffusion to Vdd power supply. Butted contacts provide a relatively dense contacting method. A method typically employed for creating butted contacts involves placing opposite diffusion blocks within the same active area, whereby the diffusion blocks do not overlap. However, this technique requires sufficient real estate in order to guarantee that both diffusion types are reliably created, thereby taking up increased area.
Furthermore, the substrate well contact diffusion, when butted against a FET diffusion, tends to create some degradation in transistor performance as the well contact diffusion gets closer and approaches the FET gate edge. It is believed that dopant diffusion of opposite species type from the substrate or well contact causes this degradation.
Accordingly, it would be desirable to provide a butted contact that requires less real estate along with eliminating or at least significantly reducing contamination of the device by dopant diffusion from the butted contact.
The present invention provides butted contacts that require reduced area along with eliminating contamination of the device from the dopants of the contact. The present invention provides for contacting an n-type diffusion to ground or a p-type diffusion to Vdd power supply. According to the present invention, the contact is vertically displaced from the top surface of the substrate.
More particularly, the present invention is concerned with a buried butted contact that comprises a substrate having dopants of a first conductivity type and having shallow trench isolation. Dopants of a second and opposite conductivity type are located in the bottom of an opening through the substrate and down to the bottom of the shallow trench isolation. Ohmic contact between the dopants of the first conductivity type and the dopants of the second and opposite conductivity type is provided on a side wall of the opening. The ohmic contact is a metallic type interconnect being a metal, metal alloy and/or intermetallic silicide. The opening overlaps the edge portion of the shallow trench isolation and overlaps a small portion of the dopants of the first conductivity type.
The present invention is also concerned with a method for forming the above-described buried contact. The method of the present invention comprises providing a substrate having dopants of a first conductivity type and having shallow trench isolation. An opening is delineated in the substrate down to the vicinity of the bottom of the shallow trench isolation and overlaps a small portion of the edge of the shallow trench isolation and a small portion of an edge of the dopants of the first conductivity type. Dopants of a second and opposite conductivity type are implanted into the bottom of the opening to thereby form a buried contact. A layer of a metallic type electrically conductive material is deposited on a side wall of the opening to provide ohmic contact between the dopants of the first conductivity type in the substrate and dopants of the second and opposite conductivity type. The metallic-type electrically conductive material is a metal, metal alloy and/or intermetallic silicide.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.